The present invention relates to systems and methods for implanting a medical device within the cardiovascular system of a subject such as a human patient.
Medical devices such as prosthetic heart valves and stents commonly are inserted by a transluminal insertion procedure. One such procedure uses a delivery system including an inner shaft surrounded by an outer shaft. The implantable device is carried on the inner shaft near a distal end of the shaft. The outer shaft has a sheath at its distal end. A proximal end of the inner shaft is fixed to the body of a handle. The outer shaft may be connected to a mechanism within the handle body. The mechanism normally holds the outer shaft in fixed position relative to the handle body, but can actuated by a control element such as a thumb wheel, lever or the like may be provided on the handle to move the outer shaft and the sheath in the proximal and distal directions relative to the inner shaft.
A guidewire is placed into the subject's vasculature through an entry point where a blood vessel can be accessed conveniently. For example, where a device is to be implanted in or near the heart, the entry point may be at the femoral artery in the subject's leg. A hollow cannula referred to as an introducer is provided around the guidewire at the entry point. The introducer cannula typically incorporates an elastomeric seal to limit blood loss during the procedure.
The implantable device is loaded onto the inner shaft, and the sheath and outer shaft of the delivery system are moved to an advanced position in which the sheath covers the device. The delivery system is advanced over the guidewire and through the elastomeric seal of the introducer and into the subject's vasculature. The delivery system is advanced through the vasculature until the device is disposed at the desired implantation site. For example, the physician may determine that the delivery system is positioned properly by observing the subject under fluoroscopic imaging and determining that an alignment marker on the delivery system or the implantable device is disposed at the proper location relative to the subject's anatomy. Once the delivery system is at the proper location, the physician attempts to hold the handle stationary while actuating the control element of the handle to retract the outer shaft and the sheath proximally relative to the inner shaft and the device. Where the device includes a self-expanding stent, the device will expand as the sheath is retracted. This action detaches the device from the delivery system and implants it in the subject.
In such a procedure, the delivery system must bend to follow the path of the guidewire through the subject's vasculature. For example, where a prosthetic heart valve is to be delivered to the vicinity of the aortic annulus of the heart, the distal end of the delivery system must bend around the arch of the aorta. To allow sufficient flexibility, the outer shaft typically has a diameter smaller than the diameter of the sheath. For example, for implantation of some prosthetic heart valves, the sheath has an outer diameter of about 18 French catheter size (about 6 mm) to provide sufficient space to accommodate the valve in its collapsed condition, whereas the outer shaft has a diameter of about 14 French catheter size (about 4.3 mm). To provide reasonable sealing against blood loss, the elastomeric seal in the introducer sheath must be sufficiently resilient to accommodate these different diameters as they are passed through the seal. Frictional engagement between the seal and the outer shaft impedes the advancing motion of the delivery system. Moreover, when the physician actuates the control element on the handle to move the outer shaft and sheath relative to the inner shaft, the frictional engagement between the introducer and the outer shaft tends to hold the outer shaft stationary relative to the subject. Thus, the handle and the inner shaft tend to move relative to the subject while the device is being exposed. This displaces the device from the desired position.
Certain delivery systems disclosed in U.S. Published Patent Application No. 2014/0005768 A1, the disclosure of which is hereby incorporated by reference herein, incorporate a sleeve that fits around the outside of the outer shaft. The sleeve has an inner diameter just slightly larger than the outer diameter of the outer shaft to provide a close but freely slideable fit. Such a device can be used in the same manner as discussed above. However, when the delivery system is advanced through the introducer, the sleeve stops at the introducer so that the sleeve seals against the elastomeric seal. The physician can continue to advance the outer and inner shafts as discussed above to position the device. The relatively close fit between the sleeve and the outer shaft impedes blood loss through this space. However, still further improvement would be desirable.